Concrete production like the production of any other man made material produced in batches requires a consistent repeatability of the properties of the product from batch to batch and even in the same batch. In the concrete manufacturing process it is extremely important to know that the properties haven't changed prior to pouring the concrete mixture.
It is generally well known that all tests performed on a fresh concrete mixture will indicate the future properties of the hardened concrete.
The industry testing standard for slump for example is found in ASTM C143 and is based on filling a cone with concrete mixture and measuring the slump of the concrete mixture as the cone is pulled out. Slump generally increases with water content of the concrete mixture or the addition of chemicals. During the concrete manufacturing process, the main problem is a control the accurate quantity of the water since water can be present in the aggregates and the measurement of the moisture percentage is not accurate. Having a mechanism to determine the water cement ratio before the concrete mixture is poured reduces the uncertainty of the quality and variation of the qualities of the product which is a part of the production process.
It is known that sensors can be used in the mixing of concrete. For example U.S. Pat. No. 6,484,079 issued to Buckelew et al. provides a global positioning satellite receiver to monitor the location of mixers. Similarly, U.S. Pat. No. 5,713,663 issued to Zandberg et al. measures the torque applied on the mixer in order to rotate it. U.S. Patent Publication Number 2012/0204625 to Beaupre et al. provides a probe that include a base and a resistance member extending from the base and onto which a resistance pressure is imparted by a rheological substance when the resistance member is submerged and moved therein. The resistance member includes an inner member and an outer member that surrounds the inner member and has a load cell connection therewith. Rheological properties can be obtained using values indicative of the resistance pressure both in a low speed range and in a high speed range. European patents EP1961538A2 and EP0924040 measure the pressure applied on a blade or on a cylinder shaped sensor attached to the wall of the truck mixer as the mixer rotates and the sensor is dragged against the concrete mixture. Zandberg et al. '663 is problematic since there are many factors that influence the torque. Accordingly, the torque measurement is not an adequate measure of the condition of the concrete mixture or slump. Also, due to fact that the stress has to be measured in one rotation speed only, important information is not measured because the concrete mixture moves in two axes, one axis being parallel to the rotation of the mixer's drum and the other axis being disposed at an angle to the first axis, by being vertical to the rotation of the mixer. Movement of the concrete mixture along the second axis is caused by the helix inside the mixer. To the best knowledge of the inventor, the previous inventions do not measure a component of a force along the second axis.
It has been found that the existing approach does not produce as good an approximation of the desired slump and does not provide the necessary information to estimate the amount of concrete mixture in the mixer or the start and finish times of the pour. Other approaches are based on installing a blade and measure the stress applied on the blade by the moving concrete mixture while the mixer drum is rotating. However, these solutions are problematic due to the concrete buildup behind the blade that, due to deterioration, affects the accuracy of the readings after some time.
Therefore there is a need to improve measurement of the concrete mixture at variable speeds.
All existing conventional applications are based on measuring the force and or the pressure applied by the concrete mixture onto the probe/sensor that is attached to the inner wall of the mixer drum while the mixer drum is rotating and the sensor is dragged through the concrete mixture.
It has been found that existing probes/sensors need to measure the average pressure/force that is applied on the probe/sensor by the movement of the concrete mixture, however, differentiating between a true measurement and the noise has been very challenging. Furthermore, it has been found that existing probes/sensors are also prone to extensive wear due to these reasons: high abrasion created by the aggregates, corrosive materials inside the concrete mixture and alkaline water. Therefore, there is an additional need to protect the sensor body from excessive wear.